1. Field of the Invention
The present invention relates to a fluoroscopic image density correction method, a non-destructive inspection method, and an image processing device capable of non-destructively inspecting for defects of welded portions of pipes in a case of welding a plurality of pipes. In particular, the present invention relates to a fluoroscopic image density correction method, a non-destructive inspection method, and an image processing device capable of obtaining the same inspection results without dependency on the skill level of an inspector for identification in images even if density irregularities occur in a fluoroscopic image.
2. Description of the Related Art
There is a known method of non-destructively inspecting for defects of welded portions of pipes in a case of welding a plurality of pipes. For example, non-destructive inspection is performed as follows. First, radiation, which originates from a radiation source and is transmitted through a welded portion of pipes, is detected by a sheet-like radiation detection medium. A fluoroscopic image, which is generated by the radiation detection medium, is read from the radiation detection medium by a dedicated scanner. The read fluoroscopic image is displayed on a display screen of a personal computer (hereinafter referred to as “PC”), and an inspector checks the image visually.
In the disclosure of JP2012-47569A, an external diameter point and an inner diameter point of a pipe are detected by using a luminance profile in a direction intersecting with the pipe in a radiation fluoroscopic image of the pipe. In the disclosure of JP1987-277542A (JP-S62-277542A), a thickness of a test pipe is calculated through density comparison by performing radiographic imaging on a monitoring pipe of which a thickness is known and the test pipe of which the thickness is unknown at the same time.
In the disclosure of JP1986-274210A (JP-S61-274210A), whether sediments are present in a measurement target pipe is measured by comparing a radiation transmission measurement pattern, which is obtained by scanning the measurement target pipe, with a radiation transmission measurement pattern which is obtained by scanning a reference pipe under the same conditions.
In the disclosure of JP2005-037193A, in non-destructive inspection, an inspection target is placed on a rotational base which rotates with predetermined angular displacement, and tomography is performed by radiation. In the inspection, an eccentricity of a central axis of rotation of the inspection target is set as a parameter, and the eccentricity, which is obtained when a sharpness of a fluoroscopic image (cross-section image) is at the maximum, is specified as an optimum eccentricity of the central axis of rotation.
In the disclosure of JP2003-190125A, there is proposed image processing for facilitating comparative reading of a plurality of medical fluoroscopic images. A frequency distribution (histogram) of density values (signal values) in a reference fluoroscopic image is calculated, the density value which has the maximum frequency in the frequency distribution is calculated as a representative value, and image processing (density correction) is performed on the other fluoroscopic images such that the representative values of the other fluoroscopic images are adjusted to the representative value of the reference fluoroscopic image (paragraphs 0049 to 0055).